Varnish treatment of electrical apparatus



July 24, 1951 R. P. HANNA ETAL 2,551,982

VARNISH TREATMENT OF ELECTRICAL APPARATUS Filed Dec. 22, 1948 2 Sheets-Sheet l Fig.|.

INVENTORS Ramond P.Hunnu,ErnestM.Loughner,

John G.Wynn and Morvln M.Fromm.

ATTOR EY July 24, 19 1 R. P. HANNA ETAL VARNISH TREATMENT OF ELECTRICAL APPARATUS Filed Dec. 22, 1948 2 Sheets-Sheet 2 Fig.2.

INVENTORS R ymond P.Honnu,Ernesi M.Luuqhnor, \V

' John G.Wynn and Marvin M'.Frornm. I68 By 2 ATTOR EY filTNESSES:

Patented July 24, i951 VARNISH TREATMENT OF ELECTRICAL APPARATUS Raymond P. Hanna, Pittsburgh, John G. Wynn, McKeesport, Marvin M. Fromm, Pittsburgh, and Ernest M. Laughner, Jeanette, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application December 22, 1948, Serial No. 66,738

4 Claims. (01. 117-49) This invention relates to the treatment of electrical members, and particularly heavy electrical members, to apply thereto an insulating varnish.

In the electrical industry, electrical members, such as magnet coils, field coils, rotors, stators and the like, after assembly are customarily treated by applying thereto a coating of insulating varnish. In many of the processes now employed for applying varnish to electrical members, an extensive amount of equipment and handling apparatus is required with considerable handling to effect a complete varnish insulating job so that the overall time for the process is lengthy. As an example, a motor stator may be loaded on a truck or put on a conveyor and then moved into a heating oven for drying. The drying operation may take many hours, often as much as from eight to twenty-four hours. Then the truck or conveyor is removed from the drying oven and the stator dipped into a varnish bath. 'In many cases, a vacuum impregnating tank is employed wherein the stator is subjected to an elaborate schedule of evacuation and varnish immersion. Thereafter, the varnished stator is drained to remove excess varnish. Finally, the stator is put back on a truck or conveyor and moved into an oven where the varnish is baked to cure it, frequently taking from eight to twenty- 'four hours for this last step. It will be apparent that the electrical members are moved and handled a number of times. For this purpose, elab- 'orate trucking or conveyor equipment, hoists and other apparatus are necessary.

One of the reasons for separating the various steps of the varnish treating process is to avoid fire hazard. Conventional heating means, such as gas burners, electrical resistance heating coils or infra red lamps, must be separated from the varnish proper in order to avoid fire hazards.

Due to the continual handling and moving of electrical members in the prior art practice of varnish treatment, there is frequent inadvertent damaging of the applied varnish film. A particular source of trouble is the bumping or scraping of the electrical members after the varnish is applied but before it is baked to a thoroughly cured state, whereby bare spots are produced. This type of damage is most prevalent in the heavier electrical members, that is, members over 100 .pounds in weight.

An object of this invention is to provide a process and apparatus for safely, rapidly and efficiently providing a cured varnish treatment of electrical members, particularly heavy members, in one continuous operation in one location using an induction coil for heating the members without handling or moving the members from the location.

Another object of the invention is to provide a process for varnish impregnating rotatable members comprising heating the members by an induction heating coil and applying varnish to the members in proximity to the induction heating coil and curing the applied varnish with heat from the induction heating coil without moving the member from a given position or handling the member during the entire process.

A still further object of the invention is to provide for varnish treating a rotatable electrical member by applying preheating and varnish-curing heating by means of an induction coil substantially uninterruptedly through the entire process.

Other objects of the invention will be in part obvious, and will in part appear hereinafter.

For a better understanding of the nature and objects of the invention, reference should be had to the following detailed description and drawings, in which:

Figure 1 is a view in elevation, partly in section of an apparatus for carrying out the process on a rotor;

Fig. 2 is a graph plotting time against temperature for a double dip varnish treating cycle;

Fig. 3 is a View in elevation, partly in section, of an apparatus for treating a stator; and

Fig. 4 is another modification of a treating device.

The present invention is based upon the feature of maintaining an electrical member in a fixed position while preheating it, or portions of it that are to be varnished, to an elevated temperature, applying varnish to the member and curing the applied varnish whereby the member trical member for heating the member substantially uninterruptedly from preheating, through the varnish applying operation and through the varnish baking or curing operation. By effecting uninterrupted heating, an optimum temperature is maintained in the member at all times during the processing and the required time for the process is reduced to the minimum.

currents and preventing corrosion. However, it is desirable that the commutator Hi and shaft i2 should not be coated with varnish since this entails a subsequent varnish cleaning operation.

The rotor I is mounted for rotation on upright supporting members 22 and 24 having bearings 23 and .25 respectively at the upper ends thereof wherein the shaft 12 may seat for rotaout the entire varnish treatment operation, we

have secured outstanding varnish treated products with substantial reduction in both time and cost of treatment.

In accordance with further features of our invention, rotatable members, and in particular, members whose exterior is substantially in the form of a surface of revolution with the axis passing therethrough, such as rotors; and stators, are mounted on a fixed bearing structure for rotation about said axis without being moved from said structure throughout the process of varnish treatment. The members so mounted are associated with a coaxial, helically arranged induction heating coil conforming to the exterior surface so that heat may-beapplied to the electrical member by energizing the coaxial induction heating coil with alternating electrical current. Heating of the electrical member can be effected by the induction coil both when the member is being rotated and when it is stationary.

Rotatable electrical members so mounted for rotation and associated with a coaxial induction heating coil may be preheated to a predetermined temperature, varnish is then applied thereto and the varnish cured without moving the electrical member from the bearing structure except for rotation thereof during the varnish impregnation and varnish curing portions of the operation.

Since induction heating can be applied to the electrical members without causing an open flame or sparking to take place, the entire operation does not constitute a fire hazard at any time, and varnish can be safely applied to the electrical member at any time during the process. If the varnish contains a volatile solvent, vapors of the solvent may be driven off safely whiletlie induction coil is heating the electrical member. Accordingly, heat may be applied by the induction coil to the electrical member substantially uninterruptedly throughout the entire process be.- ginning with preheating and through the curing of the varnish.

For one illustration of the practice of the invention, reference should be had to Figure -1 of the drawings wherein is illustrated a rotor [-0 of a dynamo-electric machine comprising a shaft 12 on which the rotor is adapted for rotation on axis A--A. The rotor includes a commutator H to which electrical windings are attached, the windings forming a front diamond portion l6 and terminate in a rear diamond and end winding portion l8. A magnetic core is disposed between the front and rear diamonds I6 and I8 andthe slot portions of the windings are disposed in the slots I9 below the outer periphery of the core 20. It is desirable that varnish should penetrate into the core 20 and pass into the slots l9 around the windings disposed therein and to cover the windings. If the windings have not been separately varnish impregnated before assemblyin the rotor, the varnish should penetrate and impregnate the insulation thereof. Also, the front and rear diamonds l6 and P8 should be thoroughly covered with varnish. The spaces between the laminations forming the core 20 will absorb some varnish thereby increasing the resistance toeddy tion. To effect rotation of the rotor It in the bearings 23 and 25 of the supporting members 2224, there is provided a pulley 25 that may be fitted on and bolted to shaft l2, with which pulley a belt 28 engages and is driven by a suitable'motor 30 or other driving means. In some instances, we

have manually turned. the shaft with a crank.

Disposed coaxially about the exterior of the rotor, is a helically wound induction heating coil 32. The turns of the heating coil 32 may be applied over the portion of the rotor comprising front and rear diamonds l5 and I8 and the core 20. Usually a few turns of the coil 32 may be disposed over the portion of the commutator to heat it and thus maintain the temperature at the, front diamond l6, which otherwise would be cooled by the mass of relatively cooler copper in the commutator. The number of turns of the coil 32 and the distribution of the turns will depend on the size and shape of the rotor, the amount of heat to be: introduced into the. rotor, and other factors which vary so widely that no precise directions can be given, but are apparent to those working in the art.

Disposed immediately below thel rotor,is a var nish pan 34. containing a supply of varnish 35. The pan 36 is mounted on a vertically movable shaft 38 which may be a hydraulic; piston so that the varnish pan 34 can be moved into. an upward position to immerse the windings- !6. and i8 and core 2?; of the rotor, and can be lowered out of contact with the rotor. It will. be appreciated that the varnish pan 34 may be elevated and lowered by pneumatic or electrical means, or even manually.

The operation of the apparatus shown in Fig. l is preferably carried out as follows. The rotor Wis-mounted on the bearings 23 and 25. of the supporting members ZIP-2t within the encircling coaxial induction coil 32 and the pulley 36. fastened to the end of the shaft l2 and connected the high frequency current field. We have found that with. ordinary silicon steel for the core, and copper conductors for the windings, a frequency of between 3000 and 5000 gives excellent overall heating results for a core with one inch deep slots. .For cores with deeper slots, lower frequencies are advisable to insure deeper heating. The major amount of the heat is developed closely to the peripheral surface of the magnetic core 20 at least to the depth of core slots I9 in the periphery. By

proper correlation of the frequency of current and the number of windings the major proportion of the heating can be localized to the portion between the outer periphery and just below theslot depth. The temperature rise is preferably controlled so that the insulation, such as'the slot cell liners and the winding insulation, is not overheated or burned. Depending upon the size the rotor, preheating may be carried out with considerable speed and usually a given temperature can be reached by use of the induction coil in a shorter time than with any other known process of heating with complete safety. For rotors weighing between 500 and 1000 pounds, we have had no difficulty in preheating them to secure a temperature of 175 C. in the windings and surface of the core within twenty minutes. The shaft I2 will be quite cool. It will be appreciated that the temperatures will vary somewhat. from point to point on the rotor and these are average temperature values. It is ordinarily desirable to. permit the rotor to soak after reaching a predetermined temperature at the core surface for a' few minutes in order to drive off any moisture and to insure that the coils, the insulation and the core are at substantially the same temperature. The rotor need not be rotated during the preheating portion of the cycle since the encircling coil heats all the parts rather uniformly. However, in practice, we have started the rotor turning at a speed of the order of from one to sixty revolutions per minute from the beginning of preheatinguntil the varnish has been applied and fully cured.

I After the windings and core of the rotor have been heated to a predetermined temperature so that the windings are thoroughly dried and in a condition to receive varnish, the varnish pan 34 is elevated to immerse the bottom portion of the induction coil 32 and the front and rear diamonds l6 and I8 as well as the core 20 to a depth of at least to the bottom of the slots in which the windings are disposed. The flow of high frequency electrical current is maintained in the coil 32 during this process and it enables the varnish to be applied without a substantial drop in the temperature of the rotor. We have been able to dip rotors in varnish with as little as eight to ten degrees drop in temperature by so continuously applying heat. There is no danger of fire by continuing heating during the varnish dip in the practice of our invention.

Ordinarily the rotors need berotated only once in the varnish although we prefer to make two the varnish pan 34 is lowered. The rotor picks up a considerable amount of varnish during the dip; but by reason of its rotation, the varnish does not drain but stays on the rotor surfaces and penetrates and soaks into the core, insulation and windings. If rotation were to be stopped, we have found that comparatively little drainage would take place. In order to prevent any varnish from collecting at the bottom of the rotor, thereby producing an unbalanced condition, rotation after clipping is desirable until the varnish sets. Accordingly, rotation of the rotor I is continued uninterruptedly from the time of dipping until the varnish sets.

Referring to Fig. 2 of the drawings, there is illustrated a typical cycle which has been carried out on a 500 pound rotor in accordance with the present invention. The preheating of the rotor required approximately forty minutes to go from room temperature to 175 C. The temperature is an average value from 6 thermocouples disposed in the core and windings. When the predetermined temperature of 175 C. was attained, the energy output of the induction coil was cut to just maintain this temperature. A dwell period of five minutes was allowed to dry out the coils 6 dipped in varnish, at the time X as shown. The

temperature of the member dropped approxi mately ten degrees centigrade during the appli-- cation of the varnish. However, by reason of the uninterrupted continuation of heating, the drop in temperature was far less than ordinarily encountered using prior art methods where temperature dropsof at least 50 C. are common. The induction coil brought the temperature of the varnish treated member up to 175 C. in about 10 minutes and thecuring of the varnish was conducted for approximately fifty minutes at this temperature. If one varnish dip is enough the member can be removed at this time. However, the. member was dipped in varnish a second time at 'the time Y with another small drop in temperature which also was recovered promptly because heating was continued. Baking for an additional forty minutes was sufficient to fully cure the varnish. The rotor was then removed from the apparatus and allowed to cool to room temperature.

The varnish may be applied to the rotor by other means than by a dip pan, for example, it maybe sprayed onto the rotating rotor In or poured on with a hose. However, for ease of operation and minimum of manual work, we have found the use of a pan M, such as shown in Fig. l, to be the most convenient method of application.

. Suitable varnishes for application to the preheated rotor are well known and may include both volatile solvent varnishes and solvent reactive or completely polymerizable varnishes. The former class may include phenol-formaldehyde, melamine, or alkyd resins, or mixtures thereof, in a partially reacted stated, dissolved in a volatile organic-material. The varnish may include from 20% to 60% by weight of the resin and the balance being a volatile solvent which must be evaporated during the baking of the varnish to cure it. It will be appreciated that thesolvent may comprise one or more volatile organic liquids with various boiling points or solvent compositions boiling over a range of temperatures. Dipping the preheated rotor in the varnish .heats up the portion of the varnish applied to the rotor, thereby reducing its viscosity and increasing its penetrating qualities. The high temperature of the rotor enables the prompt evaporation of the volatile solvent so that curing of the resin may'take place that much sooner. We find that with varnishes containing volatile solvents the preheat temperature of the rotor should be at least C. and preferably of the order-of C. and higher. We have secured ex cellent results with electrical members heated to temperatures ofbetween to 200 C.

Solvent reactive or completely polymerizable vvar'r'iishescomprise a resinous material, usually an unsaturated alkyd resin, dissolved in an unsaturated monomer capable of copolymerizing therewith under heat, or a monomer capable of reacting to a polymer, usually an allyl compound.

The present process can be employed with such completely polymerizable varnishes with excellent results. One coating of the solvent reactive varnish will give as good results as two or three separate applications of varnishes containing a 70 volatile solvent.

The present process is exceptionally well adapted to treating electrical members with organosiloxanes. The high curing temperatures required for-.. o'rganosi1oxanes, usually over 200 C.,

are detrimental to commutator insulation. By I the present process the core .2 andwindingsmay be heated to over 200 C. without heating the commutator above 150 C. An example of a suitable organosiloxane composition is phenyl methyl siloxane dissolved in toluene.

When the varnish has been applied to the rotor I0, the pan 34 is lowered and the rotor is revolved and heated by the induction coil 32 at a predetermined temperature until the solvent is driven from the varnish and the varnish is set up. Rotation can be discontinued at this time or it can be continued until the varnish is cured. It will be appreciated that varnish is ordinarily considered cured when it becomes hard enough so that the member can be handled without the varnish sticking or coming off. For some applications, the curing operation is carried out until the varnish resins have been cured to' a bonehard condition; while for other applications, the curing need not be so complete. Thus for some purposes, the varnish at the surface is cured hard, but in deep-seated portions of the coils the varnish may be only partly cured and capable of polymerizing further. The latter is particularly" true of oxidizing varnishes which depend upon oxygen from the air for completing their cure- The heating of the rotor is continued by energizin the high-frequency coil until the varnish is cured, or substantially cured as required, and then the flow of electrical current may be cut oil from the coil 32. During the cooling down of the rotor or other apparatus, curing of the varnish will continue.

Once the varnish has been cured, current flow to the induction coil 32 may be terminated and the rotor I0 allowed to cool in place and later removed from the supporting members 22 -24. However the hot rotor is preferably removed at once from the apparatus and allowed to cool in another location, so that the apparatus can be immediately employed for treating another rotor.

Referring to Fig. 3 of the drawings, there is illustrated the treatment of a stator I00 in accordance with the present invention. Thestator I00 comprises a core I02 having a hollow interior I03 in which are disposed windings I04. The stator I00 is clamped within a jig I06 comprising two U-shaped arms I08 and H0; each arm having lugs H2 in which bolts II4 are applied for clamping the stator core I00 therebetween; The jig I06 has hollow trunnions H6 and H8 for mounting in bearing supports I20, I22 for rotational movement about axis B-B. The hollow trunnion I I8 is provided with a pulley I24 driven by a belt or the like I26 as in Figur 1-. An induction coil I28 is disposed within the bore I03 of the stator so that the axis of the coil I28 is coaxial with that of the stator I00 and jig I06. Terminals I29 and I30 of the inductive coil pass through the hollow trunnions to a sourceof energy, such as a high-frequency generator or the The terminals may function to support the" like. induction coil in predetermined position. A varnish pan I32 filled with varnish I34 is mounted beneath the stator I00 and is adapted to be elevated and lowered by the arm I36-to immerse the prising a winding I52 and spool ends: I511 and,

I56 has a hollow center I56. The. coil. Iiflsisasuspended fixedly on a hanger I60 within an in? duction heating. coil I62 whereby, thecoil may be heated rapidly to a given temperature. When the coil is sufliciently heated, at varnish pan I64 containing varnish I66 is elevated by piston I60 to immerse the coil I50 and heating coil I62, thereby impregnating the coil I50. Heat is'imparted by the heating coil I62 to coil I50 throughout the immersion to maintain the coil temperature. After a short immersion the tank IN is lowered and the varnish applied to coil I50 drains briefly. The varnish left on coil I50 dries rap-' idly" by evaporation of its solvent because coil I50 is at a high temperature and the solvent tree varnish cures hard in a short time.

It will be appreciated that the induction heatingcoils 32, I26 and IE2 are usually water cooled tubing kept at a very low temperature so that no appreciable amount of varnish stays on them and the varnish does not cure on the coils.

A further advantage derived by the present process isthe better insulation obtainable thereby as an example of the results obtained, the following is a typical example of this benefit. Two: armatures, each approximately 5510 pounds in weight, were treatedthe first, in accordance with the conventional prior art practice comprising oven drying, varnish dipping and oven baking requiring a total time of twenty-six hours, and the second, in the apparatus shown in Fig. l of the drawing requiring three hours. The in-- sulation resistance was measured on both armatures with the following results:

finSliliEltiOIl es stance Condition Old Process. Process of k invention Mcpohms Meaohms As received from processing l, 440 128 hours at 50 C.,100% humidity. loss than 0. Oi) 1. 3 Dried 69 hours at 25 C. at 30% humidity less than 0. O9 21 revolution and rotatable on an axis passing.

therethrough, the member comprising a magnetic core and windings, the steps comprising horizontally and rotatably mounting the member ina fixed position for horizontal rotation on said axis within a fixed encircling induction heating coil with the of the coil being substantially on the axis of the member, energizing the coil with electrical current at a frequency of between 720 and 15,000 cycles per second to cause preheating of the member, continuing preheat-- ing untilthe windings of the member reach apredetermined temperature above C., rotating. the preheated member on said axis,.dipping the rotating member in varnish to apply a coating ofvarnish to the preheated core and the windings and continuing heating of the member by the coil whereby the temperature of the member d'oesnot drop unduly, with drawing" the rotating member from the varnish after at least one revolution of the member in the varnish, and curing r the applied varnish while rotating the-memberthe member being held in the fixed position throughout the process.

2. In the process of varnish treating an electrical member whose exterior is a surface of rev-- olution rotatable about a given axis passing therethrough, the steps comprising horizontally and rotatably mounting the member in a fixed posi-,

tion for horizontal rotation about the given axis in conjunction with an induction heating coil also disposed so that its axis is on the given axis to heat the member, energizing the coil to heat the member to a predetermined temperature above 80 C., rotating the member, applying varnish to the preheated rotating member while continuing heating it by means of the induction coil whereby the temperature of the member does not drop unduly during application of the varnish, discontinuing application of the varnish and curing the applied varnish on the member while rotating it by continuing the heating thereof by the induction coil, heat being applied by the coil substantially uninterruptedly from the start of preheating through the curing of the varnish and the electrical member being held in the fixed position throughout the process.

3. In the process of varnish treating a rotor of a dynamo-electric machine, the rotor having a magnetic core, windings and a shaft, the steps comprising mounting the rotor shaft for rotation along a horizontal axis in a fixed bearing, encircling the mounted rotor with an induction coil, energizing the induction coil with electrical current at a frequency of between 720 and 15,000 cycles per second, to cause the rotor to be preheated to a predetermined temperature above 80 C., rotating the preheated rotor in the bearing, applying varnish to the preheated rotating rotor while continuing applying heat thereto by the induction coil whereby the temperature of the rotor does not drop unduly, discontinuing application of the varnish to the rotor and curing the hollow bore, energizing the induction coil with 10 applied varnish on the rotor while rotating it by continuing the heating thereof by the induction coil, heat being applied by the induction coil substantially uninterruptedly from the start of preheating through the curing of the applied varnish the rotor being held in the fixed bearing throughout the entire process.

4. In the process of varnish treating a stator comprising a hollow axial core and windings disposed within the core, the steps comprising mounting the stator in a fixed position for rotation on a horizontal axis concentric with the axial core, disposing an induction coil within the electrical current at a frequency of between 720 and 15,000 cycles per second to cause the stator to become heated to a predetermined temperature above 80 C., rotating the preheated stator on said axis, applying varnish to the rotating stator while continuing to apply heat thereto by the induction coil whereby the temperature of the stator does not drop unduly, discontinuing the application of the varnish and curing the applied varnish on the stator while rotating it by continuing the heating thereof by the induction coil, heat being applied by the induction coil substantially uninterruptedly from the start of preheating through the curing of the varnish and the member being held in the fixed position throughout the process.

RAYMOND P. HANNA. JOHN G. WYNN. MARVIN M. FROMM. ERNEST M. LAUGHNER.

REFERENCES CITED The following references are of record in the file of'this patent:

UNITED STATES PATENTS Number Name Date 1,726,431 Fourment Aug. 27, 1929 1,967,031 Lee July 17, 1934 2,417,538 Alexander Mar. 18, 1947 

